Axcelis Technologies, assignee of the present invention, designs and sells products for treatment of silicon wafers during integrated circuit fabrication. One such product or tool is sold under the designation MC-3. This tool creates an ion beam that modifies the physical properties of wafers that are placed into the ion beam. This process can be used, for example, to dope the silicon from which the untreated wafer is made to produce a semiconductor material. Controlled use of masking with resist materials prior to ion implantation as well as layering of different dopant patterns within the wafer produce an integrated circuit for use in one of a myriad of applications.
A variety of other tools are used during integrated circuit fabrication. These tools include rapid thermal processing of wafers under controlled conditions to anneal the wafers. Other tools are used to apply photoresist in controlled patterns onto the wafers. Tools are used to remove photoresist materials from the wafers during an ashing process. Other tools are used to cut the treated wafers into individual integrated circuits.
An ion implantation chamber of an ion beam implanter such as a model MC-3 implanter is maintained at reduced pressure. Subsequent to acceleration along a beam line, the ions in the beam enter the implantation chamber and strike the wafer. In order to position the wafer within the ion implantation chamber, they are moved by a robot into a load lock from a cassette or storage device delivered to the implanter by a conveyor system or by other means of delivery.
Front opening unified pods have become a popular mechanism for moving silicon wafers from one workstation to another in an integrated circuit (IC) fabrication facility. Different versions of these pods are commercially available from different manufacturers including Asyst Technologies and Brooks Automation. A front opening unified pod (or FOUP) containing a number of stacked wafers is delivered from one tool to a next subsequent tool by an automated delivery device such as an overhead transport. The overhead transport deposits the pod to a location within the reach of a robot so that a robotic arm can extract one or more silicon wafers from the pod for treatment.
U.S. Pat. No. 5,486,080 to Sieradzki concerns a system for high speed movement of work-pieces in vacuum processing. The system employs two wafer transport robots for moving wafers from two load locks past a processing station. Additional patents relating to serial end stations are U.S. Pat. Nos. 6,350,097, 6,555,825, and 5,003,183.
Certain known ion implantation sequences require that the work-piece be implanted with ions multiple times with different ion beam formulas or recipes in a so-called chaining sequence. Chaining sequences are most efficiently performed by keeping the work-piece in the vacuum chamber for the entire sequence of recipes. The present invention concerns a transfer method and apparatus for efficiently moving work-pieces into and out of a vacuum (sub-atmospheric) chamber for work-piece processing.